Overall objectives are to 1) develop and validate new methods for studying the enterohepatic circulation of bile acids in man in health and disease; 2) characterize bile acid metabolism in health and selected diseases; 3) develop new diagnostic tests for altered bile acid metabolism; 4) explore poorly understood areas of the enterohepatic circulation. Goals for the current year are 1) Development of improved methodology--a) validation of use of 11,12-H2-labeled chenodeoxycholate in isotope dilution measurements of bile acid kinetics in man; 2) Characterization of the enterohepatic circulation, the steroid and amino acid moieties of bile acids--a) plasma disappearance of radioactivity after intravenous injection of labeled bile acids in man--b) lithocholate metabolism in man--1) biotransformation and biliary excretion of intravenously administered lithocholate, lithocholylglycine and their sulfates--2) enterohepatic circulation--3) disappearance of radioactivity after intravenous injection of labeled lithocholate and its derivatives--c) impaired lithocholate sulfation in the rhesus monkey: a mechanism for chenodeoxycholate toxicity--d) metabolism of S35-taurine in man--e) effect of deoxycholic acid ingestion on bile acid metabolism and biliary lipid secretion in healthy man; 3) Collaborative studies on patients receiving chenodeoxycholic acid for gallstone dissolution--a) increased serum sulfated and unsulfated lithocholates in gallstone patients during chenotherapy--b) effect of varying doses of chenodeoxycholic acid on bile composition in gallstone patients: a dose response study; 4) Miscellaneous studies--a) biliary bile acid composition in Wilson's disease--b) influence of primary bile acid feeding on cholesterol metabolism and hepatic function in the rhesus monkey. BIBLIOGRAPHIC REFERENCES: Korman, M.G., Ellefson, R.D. and Hofmann, A.F.: Fasting serum bile acid levels in the primary hyperlipoproteinemias. Mayo Clin. Proc. 50:76-78, 1975. Northfield, T.C. and Hofmann, A.F.: Biliary lipid output during three meals and an overnight fast. 1. Relationship to bile acid pool size and cholesterol saturation of bile in gallstone and control subjects. Gut 16:1-11, 1975.